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Waves and sound
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Sound is a wave made by vibrations. It needs something to travel through.
What is a wave?
A wave transfers energy from one place to another without moving matter along with it.
Water waves are ripples: the water moves up and down while the wave moves across. This makes them transverse waves.
Waves can reflect. When two waves meet they add together (superpose): two peaks make a bigger peak, and a peak meeting a trough can cancel out.
Water waves are ripples: the water moves up and down while the wave moves across. This makes them transverse waves.
Waves can reflect. When two waves meet they add together (superpose): two peaks make a bigger peak, and a peak meeting a trough can cancel out.
How sound travels
Sound is made by vibrating objects, such as a guitar string or a loudspeaker cone.
The vibrations pass from particle to particle. The particles vibrate backwards and forwards along the direction the wave travels: sound is a longitudinal wave.
Sound needs a medium (a solid, liquid or gas). It cannot travel through a vacuum.
Sound travels at about 340 m/s in air. It is faster in water and faster still in most solids.
The vibrations pass from particle to particle. The particles vibrate backwards and forwards along the direction the wave travels: sound is a longitudinal wave.
Sound needs a medium (a solid, liquid or gas). It cannot travel through a vacuum.
Sound travels at about 340 m/s in air. It is faster in water and faster still in most solids.
Pitch, loudness and hearing
Frequency is the number of vibrations each second, measured in hertz (Hz). Higher frequency means higher pitch.
A bigger amplitude (bigger vibrations) means a louder sound.
Humans hear roughly 20 Hz to 20 000 Hz. Dogs and bats can hear higher frequencies than we can. Sound above human hearing is ultrasound.
Sound reflects off hard surfaces (an echo) and is absorbed by soft materials like curtains.
Your eardrum and a microphone diaphragm vibrate when sound hits them. Ultrasound is used for cleaning delicate objects and in physiotherapy.
A bigger amplitude (bigger vibrations) means a louder sound.
Humans hear roughly 20 Hz to 20 000 Hz. Dogs and bats can hear higher frequencies than we can. Sound above human hearing is ultrasound.
Sound reflects off hard surfaces (an echo) and is absorbed by soft materials like curtains.
Your eardrum and a microphone diaphragm vibrate when sound hits them. Ultrasound is used for cleaning delicate objects and in physiotherapy.
You clap and hear an echo from a wall 0.5 s later. Sound travels at 340 m/s. How far away is the wall?
- The sound travels there and back.
- Distance travelled = 340 × 0.5 = 170 m
- The wall is half of that: 170 ÷ 2
Answer: 85 m
Sound is a longitudinal wave made by vibrations and needs a medium. About 340 m/s in air. Frequency (Hz) sets the pitch; amplitude sets the loudness. Humans hear about 20 Hz to 20 000 Hz.
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